The present invention relates to a process for the production of anhydrous oxime by separation of the oxime from an aqueous solution.
Oximes may be produced by reacting hydroxylamine with: hexachlorocyclopentadiene as taught by U.S. Pat. No. 3,141,043; cyclic halogenated olefins as taught by U.S. Pat. No. 3,459,802; imino-amines as taught by U.S. Pat. No. 3,462,488; or nitriles as taught by U.S. Pat. No. 4,256,899. Oximes are most generally produced by reacting an organic carbonyl compound such as an aldehyde or ketone with hydroxylamine generated from a hydroxylamine salt such as hydroxylamine sulfate or hydroxylamine chloride. The more economical processes use hydroxylamine sulfate or chloride as aqueous solutions as taught by commonly assigned U.S. Pat. Nos. 3,873,624; 3,931,331; 4,237,069; and 4,323,706; as such, the produced oximes need to be separated from the aqueous system and dried. The need to dry the oxime is more imperative in situations where the oxime is to be used in applications which require anhydrous conditions such as isocyanate condensation and carbamate formation.
Generally, oximes are not very thermally stable and the stability is adversely affected by the presence of acids and bases as well as salts. Two standard processes for the production of anhydrous oxime include: liquid-liquid separation of the water-immiscible oxime from the aqueous oximation mass followed by distillation of the removed oxime phase under reduced pressure to recover the oxime; and liquid-liquid extraction of the aqueous oximation mass with a suitable water-immisible organic solvent followed by distillation of the organic extract to separate the solvent and recover the oxime as mentioned in U.S. Pat. No. 3,141,043. Such distillation operations encounter build-up of inorganic salt which is carried forward sa salt solution with the oxime to the distillation pot. Heating oxime by itself in the presence of salt can cause the oxime to decompose, and in some instances, decompose so violently so as to explode. As such, the two aforementioned processes for the production of anhydrous oxime are disadvantageous.
If the oxime is partially miscible in water, a standard process for the production of anhydrous oxime involves at least two distillations. In the first distillation, an oxime-water mixture vapor boils over and upon condensation, a two-phase condensate forms; in the second distillation, the water is boiled off and the oxime is recovered. This process is disadvantageous because two distillations are required.
For low boiling oximes such as acetone oxime and acetaldoxime which are freely soluble in water, the task of producing anhydrous oximes by separating the oxime from the aqueous phase is even more difficult because such oximes distill over as water-miscible azeotropes.
Because the aforementioned hazards and difficulties exist in standard processes for the production of anhydrous oxime by separation of oxime from an aqueous phase, a need exists for a simple process for the production of anhydrous oxime by separation of oxime from an aqueous phase wherein the foregoing hazards and difficulties are eliminated.